Traveling wave tube



May 10, 1960 T. E. EVERHART 2,936,395

TRAVELING WAVE TUBE Filed Sept. 30, 1955 2 Sheets-Sheet 1 May 10, 1960 t T. E. EVERHART 2,936,395

TRAVELING WAVE TUBE Filed Sept. 50, 1955 2 Sheets-,Sheet 2 MMA/FWHM United States Patent O i 2,936,395 TRAVELING WAVE TUBE Thomas E. Everhart, Santa Monica, Calif., assgnor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application September 30, 19'55, Serial No. 537,744

8 Claims. (Cl. S15-3.5)

This invention relates to traveling-wave tubes and more particularly to apparatus for coupling radio frequency energy to a traveling-wave tube having a stub-loaded, contrawound slow-wave structure.

In the application entitled Laminated Slow-Wave Structure, Ser. No. 537,646, filed concurrently herewith and assigned to the same assignee by I I. Caldwell, there is therein disclosed and taught a laminated slow-wave structure which is built up from thin stampings of appropriate shape stacked or assembled along aligning rods and brazed together. In utilizing such a slow-wave structure and realizing its many advantages, special coupling and matching problems are encountered in launching a traveling-wave thereupon from an external microwave transmission line.

It is therefore an object of the present invention to provide matching apparatus for coupling microwave energy to a laminated slow-wave structure in order that one may utilize the advantages of such a slow-wave structure.

Briefly, in accordance with this invention an evacuated section of waveguide or coaxial transmission line is directly coupled to a portion of the simulated contrawound helix disclosed by Caldwell, op. cit. and is adapted to launch traveling waves upon this slow-wave structure with a minimum of reections back into the transmission line.

The novel features which are believed to be characteristic of this invention both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

In the drawings: I

Fig. 1 is an elevational view partially in section taken along the center line of a traveling wave tube embodying a matching scheme in accordance with this invention; and

Figs. 2, 3, 4, and are sectional views also taken along thecenter line of portions of alternative embodiments of the present invention.

`For purpose of description of the structure of this invention each of the gures is a section taken so that the axis of the feeding microwave transmission line is in the plane of the drawing.

VReferring now to Fig. 1, traveling-wave tube 10 is shown comprising an electron gun 12, a slow-wave structurel 14 and a collector electrode 16 with appropriate voltage sources as illustrated. Slow-wave structure 14 embodying a composition of thin stampings is assembled inaccordance with the teachings of the above cited application of Caldwell and in a manner such that stubs 18 are aligned normal to the surface of the drawing and into the paper. Alternate stubs coming out of the paper (not shown) extend into the spaces designated 20. A

waveguide 21 is provided for feeding electromagnetic wave energy to slow-wave structure 14 and includes a section 22 passing along the end of slow-wave structure 14. Matching ferrule or cylinder 23 is attached to one wall of waveguide 21, and according to this example, is in length approximately the height h of the waveguide; although ferrule 23 may -be of any length shorter than h. Opening 24 in waveguide 22 corresponds in diameter to the inner diameter of cylinder 23. A shorting plane in the form of an iris 2.6 is secured across the opening. of slow-wave structure 14 to preclude undesired waveguide propagation along that space outside the slow-wave structure. An adjustable shorting plane 28 is mounted in stub 30 being an extension of waveguide 22 to optirnize the waveguide match.

In like manner waveguide 32 which may be identical to waveguide 21, may be coupled to the opposite end of slow-wave structure 14. A solenoid 33 substantially surrounds the traveling-wave tube to constrain and focus the electron beam along and within the simulated helix of slow-wave structure 14. A pressure seal 34 transparent to electromagnetic energy is provided in flange 35 of waveguide 21 and may be an arched glass window.

Referring to Fig. 2, the sectional View shown is taken through slow-wave structure `14 which has been rotated 90 about its axis with respect to the view shown in Fig. l; thus in this embodiment stubs 18 and 20 lie in the plane of the drawing, and the inner conductor 35 of a coaxial transmission line 36 is coupled to the rst loading stub 18. Shorting iris 38 isolates the electron gun but permits passage of the electron beam.

Referring to Fig. 3 the rst loading stub 18 instead of being coupled to the inner conductor of a coaxial line projects into a waveguide section 40 and excites therein a microwave mode of propagation or furnishes the coupling to launch a traveling-wave upon slow-wave struc-` ture 14. Again in Fig. 3 a shorting iris 38 isolates electron gun 12.

Referring to Fig. 4 there is shown an alternative em-` ibodiment utilizing a section of ridge waveguide 42 hav-- ing ridges 44 and 46 which project into the region at: the end of slow-wave structure 14 and are coincident with the first two loading stubs 18. The left hand wall of waveguide section 42 projects across the traveling wave tube to form a shorting iris permitting passage of the electron beam.

Fig. 5 is a modification of the structure of Fig. 1. In accordance with this embodiment however, matching ferrule or cylinder 22 is relatively shorter than ferrule 2.2 in Fig. l. few loading stubs which are designated 181 and 20 and which are tapered as shown. The loading stub furthest to the left is secured to cylinder 22. Again as in Fig. l waveguide stub 30 may have an adjustable shorting plane 28 for optimizing the waveguide match.

There have thus been disclosed several embodiments of a system for coupling microwave energy to or from a traveling wave tube having a laminated contrawound slow-wave structure. Although the slow-wave structure shown in each of the views is a unifilar contrawound helix, it is obvious that multilar configurations might also be utilized without departing from the scope and spirit of the present invention.

What is claimed is: l

1. A traveling-wave tube comprising: a laminated slowiwave structure including a plurality of conductive, subtoward said axis, and external microwave transmission Patented May 10, 1960` Waveguide section 21 lthus encloses the irst means coupled to at, least, one ot said loading stubs oi the slow-wave structure in a manner such that microwave energy propagating in said transmission means launches travelingwaves onr said slow-wave structure, by transmitting microwavefenergy through said at .least` one' of said loading stubs.

2.. A- traveling-wave tube includingV a laminated stub;- loaded sloW-wawe structure comprising, a plurality of. substantially planar metal-lic members disposed perpendicularly to and stacked along the longitudinal axis of said tube, at least some of said planar members each having. a loading stub extending from its periphery toward said axis, apparatus for coupling. microwave energy to the slow-wave structure, said apparatus comprising: a matching, ferrule connected to one of said loadingstubs ofthe slow-wavestructure;waveguide means disposed inv microwave excitation relationship with said matching ferrule andat least one of said stubs in a manner such that microwave energy propagating in said waveguide means launches a traveling ywave upon said slow-wave structure.

3. A traveling-wave tube including a laminated stubloaded slow-wave structure comprising a plurality of substantially planar metallic members disposed perpendicularly to and stacked along the axis of said tube, at least one of said planar members having a loading stub extending from its periphery toward said axis, apparatus for coupling microwave energy to `the slow-wave structure, Said apparatus comprising: coaxial waveguidey means having an outer conductor coupled to the outer wall of the slow-wave structure and having an inner conductor coupled iny microwave energy exchange relationship to one of. the loadingjstubs of the'slow-wave structure in a man-Y ner.. such that microwave energy propagating in. said coaxial waveguide means launchesl traveling waves upon said slow-wave structure.

4. A. traveling-wave tube, including a laminated stubloaded slow-wave structure comprising a plurality of substantially planar metallic members disposed perpendicularly to, and stacked along the axis of said tube, at least some of said members each having a' loading stub extending from the periphery of said member toward said axis,v apparatus for coupling microwave energy to said slow-wave structure,y said apparatus comprising rectangular waveguide means disposed with one of its longitudinal-walls contiguous to one wall ofv said slow-wave structure and having an openingin said longitudinal wall of said rectangular waveguide means, one of. said loading. stubs-of. said slow-wave structure having an extension protruding through a wall of said slow-wave structure and -thence through said opening in said longitudinal wall of said waveguide means in a manner such that microwave energy propagating in. said wave-guide means couples microwave energy through said extension to said slowwave structure thereby to launch traveling waves upon said slow-wave structure.

5.V A traveling-wave tube, including a laminated stubloaded slow-wave structure comprising a plurality of substantially planar metallic members disposed perpendicularly to and stacked along the axis of said tube, some of said planar members each having a loading stub extending from the periphery of said planar member toward said axis, apparatus for coupling microwave energy to said slow-wave structure, said apparatus comprising rectangular waveguide means disposed perpendicularly to the slow-wave structure and having ridges extending into the slow-wave structure in a mannerV to form. extensions of two of said loading stubs of the slow-wave structure such that microwave energy propagating in said waveguide meansv causes the launching of traveling waves in the slow-wave structure.

6..In a traveling-wave tube having a rectilinear axis along which an electron stream is projected, a laminated stub-loaded slow-wave structure comprising a plurality of...substantially planarmetallic members disposed perpendicularly to. said. axis, apparatus. for coupling` microwaveenergy to said slow-wave structure, said apparatus comprising rectangular waveguide means disposed perpendicularly to the slow-wave structure and parallel to the loading stubs thereof, said waveguide means traversing a portion of the slow-wave structure including a plurality of the loading stubs and said waveguide means being disposed in microwave energy exchange relationship with saidplurality of the loading stubs whereby saidrrrlicro-V` wave energy propagating in said waveguide means is` radiated onto saidplurality of loading stubs thereby to cause the launching of traveling waves upon said slowwave structure,

7. ln a traveling-Wave tube having a rectilinear axis `along which is projected an electron stream a laminated stub-loaded slow-wave structure comprising a plurality of thin, substantially planar metallic stampings disposed perpendicularly to said axis, apparatus for coupling microwave energy! to the slow-wave structure, said apparatus comprising rectangular waveguide means disposed perpenl dicularly to said slow-wavey structure and parallel to the? loading stubs thereof, said waveguide means traversing a portio'noftheslow-wave structure including a pluralityofthe loading stubs and said waveguide means being dis'- posed' inl. microwave energy exchange relationship with said-` plurality of. the loading stubs the outer ends of said; plurality the stubs being tapered in a manner suchv that; their lengths are greater 'across said rectangular Waveguide meanstowardthe center position of said slow-wave structure said microwave energy propagating in said: waveguide means being radiated onto said plurality ofiV loading stubs to launch traveling waves upon said slowwave, structure.

8'. In: a traveling-wave. tube having a rectilinear axis: along which is projected an electron` stream, a laminated stub-loaded slow-wave structure comprising a plurality' of thin, substaintially planar metallic stampings disposed perpendicularly to said axis, apparatus forV coupling microwave energy to the slow-wave structure,l said apparatus; comprising `rectangular waveguide means disposed perpendicularly to saidislow-wave structure and parallel to the loading stubs thereof, a matching ferrule connected to one wall of said/"waveguide means and to oneV ofv said loading stubs, said waveguide means traversing a por-1 tion of said slow-wave structure including a plurality of said loading stubs and said matching Yferrule and being disposed in microwave energy exchange relationship there-- with said plurality of loading stubs being tapered suchV that their lengths increase across said rectangular Waveguide means away from said matching ferrule and toward the center position of said slow-wave structure said microwave energy propagatingin said waveguide means being; radiated onto said plurality of loading stubs and matching'-` ferrnle: to launch traveling waves upon saidV slowwave-- structure.

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